In a storage system having a cluster configuration where a plurality of storage nodes are collected, the storage nodes are driven in parallel so that high performance of data access can be implemented due to parallel access and high availability can be implemented due to data redundancy. Hereinafter, in description and drawings, the storage node may be referred to as a node.
Recently, a data transfer amount between nodes is increased according to an increase in the number of nodes, and performance of the storage system is deteriorated because of a lack of a band of a network which couples the nodes. Methods of solving the problem are known as follows.
In a first method, a local cache is used (for example, PTL 1). In this method, in a cluster configuration where a plurality of storage apparatuses (nodes) are coupled through a network, when a data write request from a host is received, data are temporarily stored in the local cache. The local cache denotes a cache in a node having write destination volume. Since data are temporarily stored in the local cache, the number of times of data transfer through the network from the cache to the write destination volume is reduced, so that the data transfer amount between the nodes is suppressed.
In a second method, a dynamic capacity allocating function is used (for example, PTL 2 and PTL 3). The dynamic capacity allocating function is implemented by a capacity pool configured by collecting storage areas of a storage node and a virtual volume. The virtual volume denotes a volume having no physical storage capacity. In the dynamic capacity allocating function, a node receiving a data write request allocates a portion of a capacity space of the capacity pool as a storage area to storage destination sites of write data in the virtual volume when data writing in the virtual volume occurs. In this case, in the node receiving the data write request, the storage area is allocated, and data are stored in the allocated storage area, so that the number of times of data transfer through the network is reduced, so that the data transfer amount between the nodes is suppressed.